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i recently bought my 1997 540i. aaaand. the problems begin. i suspected there was a leak. since i found drops under my car. turns out it was coolant, surprise surprise. however i cant seem to find the source.

the v8's in the 540's X5's are notorious for intake valley pan and intake seal leaks. When the valley pan leaks its accompanied by coolant. intake gasket seals are identified by rough idle or missing on acceleration. I suspect it is the valley pan leaking which is beneath the intake. Not an uncommon procedure or problem for that matter. a bit pricey to fix. Worse case scenario is the head gasket but you would then find possible coolant in the oil and lots of white smoke pushing out the tail pipe.

The majority of leaks in this are tend to be from a cracked coolant expansion tank or the sensor that plugs in the bottom of it. With the plactic belly pan in place it could be from some where else as well so you may want to remove the belly pan to help find the leak.

I've noticed something similar starting to take place with mine on the passenger side.

It doesn't appear to be the expansion tank or the sensor at the bottom of it or the passenger side drain plug on the block either. All those areas are bone dry with no signs (dry stains) that leak took place at either of these locations.

The passenger side of my oil pan and the ac compressor are wet as well as the fan belt tensioner (mini shock absorber like) on the lower passenger side.

I think it maybe the waterpump but I can't trace the leak back to it. Waterpump leaks have a way of hiding themselves by traveling to other parts of the car and appearing to come from that area.

Nope. Never solved the mystery of the coolant leak. At first I thought it was just a crack in the expansion tank. But after a while I noticed I wasn't losing any more coolant so I just forgot about it. Should check sometime soon though.